Nowadays on the medical delivery device market, there are numerous devices for delivering medicament and also patented where the medicament is arranged in a container, such as a syringe, cartridge and the like, and wherein the medicament is exposed to pressure when it is to be delivered. The most common design is a generally tubular compartment having a stopper in one end of the compartment and a delivery opening e.g. a needle, attached to the opposite end of the compartment.
In order to deliver a quantity of medicament, the stopper is exposed to pressure, i.e. pushed into the compartment by a plunger rod, which could be done manually by a finger of a physician or trained person, which is the case for simple handheld hypodermic syringes.
In many instances it is desirable to be able to deliver multiple specified quantities of the medicament on multiple delivery sites in a stepwise mode. This is for example the case with manually operative mechanisms for moving a plunger rod as disclosed in the International Application Publication WO2006/020756 A2 and in the U.S. Pat. No. 4,512,767. The problem of said devices resides in the accuracy of the doses. If the actuation button is not fully depressed smaller doses cannot be delivered. Another example is the case with a multi-dose injection device, which is capable of delivering a number of specified, set doses until the compartment is empty, as disclosed in the European patent application No. 05104734.8 where specific doses can be set before injection. The injection device disclosed in said European patent application is arranged with spring means for exerting a pressure on the medicament for delivering a specific dose, i.e. pushing the plunger rod and thus the stopper into the container. The delivery of a dose requires a certain force from the spring means in order to overcome the friction between the somewhat resilient stopper and the inner surface of the container and also to be able to press the medicament in liquid form through a rather small passage in the needle, possibly within a predetermined time.
Typically, when a medicament/substance is to be delivered in multiple predetermined small quantities on multiple delivery sites in a stepwise mode, said medicament/substance quantities are injected manually, i.e. a normal type of syringe is used. In some treatments said medicament/substance has a high viscosity. Because of the rather large forces required for injecting said substances, and also due to the many small injections needed for a treatment, it is tiresome for the operator to use such a syringe during a treatment. The problem of the device disclosed in the European patent application resides in the degree of ergonomics when the medicament is to be delivered in multiple predetermined quantities on multiple delivery sites in a stepwise mode.
Moreover, a further example is the case with a multiple, metered dosage dispensing device as disclosed in the U.S. Pat. No. 4,659,327; wherein the device comprises an elongated body with an ampule containing material to be dispensed, a piston movable against the material to discharge from a nozzle, a ribbed plunger rod linearly movable by a pressure device against the piston to discharge material and an stop and release toothed unit movable intermediately of the ends of the body between a depressed and an undepressed position respectively to engage a pair of racks of teeth on the ribbed plunger rod. When said stop and release toothed unit is depressed, said unit allows the plunger and the piston to move linearly a predetermined increment, to stop said movement and to maintain the plunger in a stopped position until the unit is depressed again. The problem of the device disclosed in the U.S. Pat. No. 4,659,327, resides especially in the possibility of delivering accurately very small doses, as in the range of 0.01 ml.-0.005 ml., since the plunger rod, which is not adapted to be rotatable, and the stop and release toothed unit are designed having a gearing which is not adapted for such small doses.
There are thus a number of aspects that are addressed with the present invention.